Research and development of polymer-clay nanocomposites wherein dispersion of swelling layered silicates composed mainly of clay minerals are controlled at nanometer level are being performed actively as means of improving heat resistance, rigidity and gas barrier of polymer materials. Swelling layered silicates such as smectite, which are one kind of clay minerals, have ion-exchangeability and swelling property for water due to hydration of ions between the layers.
Recently, swelling fluorine mica that has Na, Li and the like between the layers has been obtained artificially and used in polymer-clay nanocomposites. This swelling fluorine mica is higher crystalline and has larger particle forms than smectite, however, it is in the microcrystal form compared with non-swelling mica minerals naturally produced.
Complexing smectic swelling layered silicates with polymer materials does not result in well-performed reinforcement effect generated by complexing because its hydrophilic nature decreases dispersion of hydrophobic polymers. Therefore, polymer-clay nanocomposites are produced by inserting (intercalating) beforehand between layers organic molecules that have high affinity with the matrix polymers or monomers that is to be raw materials of the polymer materials, and performing organizing treatment followed by complexing or polymerization between layers with polymer materials.
Specifically, for swelling layered silicates that have undergone organizing treatment, a number of studies have been done and there are reports for various systems including not only organic-inorganic composites of alkyl ammonium and smectite (Nonpatent Literature 1), but also composites of diammonium compounds or heteroaromatic cations with swelling layered silicates (Patent Documents 1 and 2), composites of alkyl amines with swelling fluorine mica (Patent Document 3) etc.
Further, for polymer-clay nanocomposites, a method wherein organic clay is added in any step in producing polyamide forms (Patent Document 4), polyamide compositions wherein cation exchangeable layered silicates are ionic bound and methods for producing them (Patent Documents 5 and 6), as well as polyamide compositions and thermoplastic resin compositions wherein swelling fluorine mica that has undergone organizing treatment (Patent Documents 7 and 8) is used and methods for producing them have been proposed. On the other hand, it is generally recognized that mica clay minerals and mica minerals wherein ions between the layers are K ions are non-swelling and nonion-changeable. It is considered that this non-swelling property is caused by electrostatic crosslinking effect of K ion fitted in the hexagonal ring of oxygen on the surfaces of two sheets (e.g. Nonpatent Literature 2).    Non-patent Literature 1: MacEwan, D. M. C. and Wilson, M. J., Interlayer and Intercalation Complexes of Clay Minerals, In “Crystal Structure of Clay Minerals and their X-ray identification” Brindley G. W., Brown, G editors, London: Mineralogical Society, (1980) 197-248    Non-patent Literature 2: H. van Olphen, Chap. 5 Clay Mineralogy, III. ILLITE (NONEXPANDIND 2:1 LAYER CLAYS), In “An Introduction to Clay Colloid Chemistry: for clay technologists, geologists, and soil scientists” 2nd ed, New York: Wiley, (1977) 68-69    Patent Document 1: Japanese Patent Laid-Open No. 63-242915 (Japanese Patent Publication No. 5-74526)    Patent Document 2: Japanese Patent Laid-Open No. 8-337414)    Patent Document 3: Japanese Patent Laid-Open No. 59-223218 (Japanese Patent Publication No. 2-27282)    Patent Document 4: Japanese Patent Laid-Open No. 48-103653    Patent Document 5: Japanese Patent Laid-Open No. 51-109998    Patent Document 6: Japanese Patent Laid-Open No. 62-74957    Patent Document 7: Japanese Patent Laid-Open No. 08-134205    Patent Document 8: Japanese Patent Laid-Open No. 2000-053805